Procedure and means for replacing and procedure for repairing a section of a pipe in the primary circuit of a nuclear reactor

ABSTRACT

In a nuclear reactor, cooled by pressurized water, an apparatus is employed for replacing a section of a primary circuit primary pipe that interconnects first and second components of a primary circuit. The apparatus cuts out and removes a section of the primary pipe. Supports are provided for the end parts of a new replacement section in a position held by the removed pipe. The apparatus bevel welds the end parts of the new replacement section of the primary pipe to confronting corresponding ends of the remaining primary pipe. Means are provided to work within the pipe along the entire length of the interior surface of the primary pipe and is introduced through one of first and second components of the primary circuit to a location within the welded replacement pipe section.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 10/394,219, filed Mar. 24, 2003.

TECHNICAL FIELD

The invention relates to a procedure and means for replacing a sectionof pipe in the primary circuit of a nuclear reactor cooled bypressurised water and in particular the replacement of a section of acold leg in the primary circuit.

BACKGROUND TO THE INVENTION

Pressurised water reactors include a primary circuit through whichcirculates the water cooling the core of the nuclear reactor locatedwithin the reactor vessel so as to transfer the heat drawn from the coreof the nuclear reactor to the feed water which is heated and vapourisedwithin the steam generators. The primary circuit of a pressurised waterreactor includes at least one loop and generally several loops (three orfour) in each of which is provided a steam generator and a primary pumpwhich circulates the primary coolant between the reactor vessel and thesteam generator. Each of the loops in the nuclear reactor's primarycircuit comprises three main large diameter pipes, each of which connectto components of the primary circuit. A first large diameter pipe, orhot leg, is connected to the vessel on the one hand and a primary partof the steam generator on the other at an inlet compartment to the waterchamber of the steam generator, and transfers water heated in contactwith the core in the reactor vessel to the steam generator. A secondpipe, called the cross-over leg, links an outlet compartment from thewater chamber of the steam generator to an inlet pipe for the volute ofthe primary pump. A third large diameter pipe or cold leg provides alink between the outlet pipe from the volute of the primary pump and thereactor vessel. Cooling water cooled in the steam generator and drawn inby the primary pump is delivered to the reactor vessel to cool the corethrough the cross-over leg, the primary pump and the cold leg.

Auxiliary and back-up circuits are associated with the primary circuitto perform particular functions, either during normal operation of thenuclear reactor, or during shutdowns, or again in the course ofincidents or accidents.

In particular a chemical and volume control circuit (RCV circuit) isconnected to the pipes of the primary circuit to control the quantity ofwater present in the primary circuit, in particular by making periodicalmake-up injections, and the chemical composition of the reactor coolingwater, which contains various additives, by sampling the primary waterand re-injecting, into the primary circuit, water containing additivesin the requisite quantity to ensure the required composition of thecooling water.

Among the back-up circuits associated with the primary circuit, thesafety injection circuit (RIS) injects a large flow of pressurised waterinto the primary circuit if there is a major water loss which cannot becompensated for by the RCV circuit.

The auxiliary and back-up circuits associated with the primary circuitcomprise pipes having a very much smaller diameter than the diameter ofthe primary pipes, and these are connected to the pipes of the primarycircuit through branch connections.

In particular, the RCV circuit, which consists of three inch (76 mm)pipe, is connected to the cold leg by a branch connection in a part ofthe cold leg located close to the outlet pipe from the volute of theprimary pump. Water in the RCV circuit is reinjected into the primarycircuit through the cold leg branch connection with the result that theinner surface of the cold leg in this reinjection area is subjected toflows of water at possibly very different temperatures depending uponthe operating status of the reactor and the RCV circuit.

Some defects have been observed on the inner surface of the cold leg inthese cold leg reinjection areas due to the circulation of flows ofwater at different temperatures, these defects being known by the nameof “crazing”.

Although these defects only affect a superficial part of the innersurface of the cold legs, for safety reasons it has been felt necessaryto sample sections of the cold-leg affected by crazing for expertassessment, and for isolated or possibly systematic replacement of coldleg sections in the light of the results of the expert assessments.

The sections of cold leg which are sampled have a first end adjacent tothe outlet pipe from the volute of the primary pump and a second endproviding a connection between two successive welded sections formingthe cold leg. A section of this type bounded as described above isapproximately 3500 mm long and includes various branch connections inaddition to the branch connection for a feed pipe to the RCV circuit, inparticular a branch connection to the auxiliary spray line and the spraycircuit of the pressuriser which controls pressure in the primarycircuit.

Conversely the section which has to be replaced does not include theconnection to the RIS circuit, the cut opposite the end of theconnection to the volute of the pump being made upstream of theconnecting pipe to the RIS circuit.

Procedures for replacing the components of a primary circuit of anuclear reactor and in particular procedures for replacing steamgenerators in which the pipes of the primary circuit are cut and thepipes of a new replacement steam generator are connected to the cutpipes of the primary circuit by welding are known. After the pipes havebeen cut and the connecting surfaces between the pipes and thereplacement steam generator pipes have been machined, the steamgenerator is placed in position so that the connecting surfaces formbevels between them, through the full thickness of the pipes andbranches, into which weld metal is laid on the-outside of the pipes andthe bevel using a process of the orbital TIG type. Generally narrowbevel welding is performed, that is to say metal is deposited on a bevelof small width, generally less than 15 mm, in which the oppositesurfaces form a very small angle, less than 5°, between them.

Where such a component replacement is made, the welds are made underconditions which are the same as those used when a steam generator isinitially fitted and they do not therefore have any special featureswhich require additional inspection or machining over and above thoseperformed in the operation of incorporating a steam generator into anuclear power station when under construction.

Conditions are completely different when a section of pipe, and inparticular a section of a cold leg, is replaced in the primary circuitwhich is an operation involving restoration of part of the pipe itself.

Hitherto no procedure and means have been known to ensure optimumconditions for replacing a section of a primary pipe.

SUMMARY OF THE INVENTION

The purpose of the invention is therefore to provide a procedure forreplacing a section of the primary circuit pipe of a nuclear reactorcooled by pressurised water connecting a first and a second component inthe primary circuit of the nuclear reactor in which identification ofthe cuts which have to be made, cutting of the section at its ends,removal of the section, bevelling of the joining ends of the partremaining after the section of the primary circuit pipe has been cutout, adjustment of the new replacement section for length and bevellingof the joining ends of the new replacement section, and fitting andbevel welding the joining ends of the replacement section to the ends ofthe remaining parts of the pipe are effected from outside the pipe, thisprocess ensuring perfect quality in the junction zones of thereplacement section.

With this object machining and inspection of an inner part of thejoining ends which are welded together is also carried out within thepipe, by remote control and by remote operation or in a programmed way,by introducing and inserting means for working within the pipe from oneof the first and second components of the primary circuit.

The invention also relates to a procedure for the repair of a defectivesection of pipe in the primary circuit of a nuclear reactor cooled bypressurised water connecting a first and a second component of theprimary circuit of the nuclear reactor, wherein the work of inspection,machining and filling by welding is also carried out within the pipe, byremote control and remote manipulation or in a programmed way, byintroducing and inserting means for working within the pipe from one ofthe first and second components of the primary circuit.

Finally the invention relates to means which make it possible toimplement the procedure according to the invention, in particular forcarrying out the operations of machining by grinding, inspection and ifnecessary repair of the junction zones of a replacement section for aprimary circuit pipe of a pressurised water reactor.

BRIEF DESCRIPTION OF DRAWINGS

For a proper understanding of the invention a procedure for replacing asection of a cold leg in the primary circuit of a nuclear reactor cooledby pressurised water and means which can be used to effect machining andinspection within the pipe for implementing the procedure according tothe invention will now be described by way of example with reference tothe appended figures.

FIG. 1 is an exploded perspective view of the safety containment and theprimary circuit of a pressurised water reactor.

FIG. 2 is a view in cross-section along a horizontal plane of a loop ofthe primary circuit of the nuclear reactor.

FIG. 3 is a simplified view in elevation of the primary pump and thesection of the cold leg of the primary circuit which has to be replaced.

FIG. 4 is a cross-section view in a vertical plane along 4—4 in FIG. 3.

FIG. 5 is a view in vertical cross-section of the top of the primarypump bunker beneath which lifting and handling means are located toimplement the procedure according to the invention.

FIG. 6 is a view in vertical cross-section illustrating the supports onthe cold leg for implementing the procedure according to the invention.

FIG. 7 is a view in cross-section of the volute of the primary pumpduring an initial stage of the replacement procedure according to theinvention.

FIG. 8 is a diagrammatical exploded perspective-view showing thehandling means located above the volute of the primary pump forimplementing the procedure according to the invention.

FIG. 9 is a view in cross-section through a vertical plane of the voluteof the primary pump fitted out for implementation of the procedureaccording to the invention through the inside of the volute of theprimary pump and the cold leg.

FIG. 10A is a diagrammatical perspective view illustrating the handlingoperations required for fitting the new replacement length of the coldleg in the primary circuit.

FIG. 10B is an exploded perspective view illustrating a further stage inthe fitting of the replacement section of the cold leg.

FIG. 11 is a side view in elevation and partial cross-section showingthe devices for holding the new replacement section of the cold leg forwelding the replacement section.

FIG. 12 is a diagrammatical exploded view in perspective illustrating anoperation of inserting means for working within the cold leg from thevolute of the primary pump.

FIG. 13 is an exploded perspective view of the volute of the primarypump showing the protection and guidance and support means for insertingthe means for working within the cold leg from the primary pump.

FIG. 14A is an exploded perspective view of the means for carrying outthe work.

FIG. 14B is an exploded perspective view of the carriage for moving themeans for working in the cold leg.

FIG. 15 is an exploded perspective view showing the means for carryingout work in the course of an operation for machining the inside surfaceof a connection weld in the cold leg.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows the containment building 1 of a pressurised water reactorhousing primary circuit 2 which in the situation illustrated in FIG. 1is a circuit having three loops, each of the loops having connectingpipes from a steam generator 3 and a primary pump 4 to reactor vessel 5enclosing the core comprising fuel assemblies.

Each of the loops in the primary circuit has a first pipe 6, called thehot leg, which provides a link between the reactor vessel and the inletto the primary part of steam generator 3, a second pipe 7, or cross-overleg, providing a link between the outlet from the primary part of steamgenerator 3 and the inlet to volute 9 of primary pump 4, and a thirdpipe 8, or cold leg, providing a link between the delivery outlet fromvolute 9 of the primary pump and the reactor vessel.

Water cooling the reactor circulates within the vessel in contact withthe core assemblies, which causes it to be heated. The heated water isdelivered by hot legs such as 6 to the primary part of the steamgenerator to be distributed to the exchanger tubes of the steamgenerator bringing about the heating and vapourisation of secondary feedwater and cooling of the primary water. The cooled primary water isrecovered in the outlet part of a water chamber of the steam generator,and then via cross-over legs 7 in which the cooling water is drawn alongby primary pump 4. The cooling water drawn into volute 9 of the primarypump is delivered to cold leg 8 through the delivery pipe of volute 9 tobe reintroduced into a part of the vessel which ensures that coolingwater is delivered to the core of the nuclear reactor.

Above volute 9, in which the pump's impeller is fitted, the primary pumphas a drive assembly for the pump impeller comprising an electric motorand means for cooling and insulating the motor.

On one of the loops the primary circuit also has a pressuriser 11 whichensures that the pressure and temperature of the cooling water in theprimary circuit are maintained. The water in the primary circuit is at apressure of the order of 155 bars and a temperature of 320° C. while thenuclear reactor is in operation.

The reactor building, within safety containment 1, incorporatesdifferent means of access to the components of the primary circuit anddifferent handling means such as revolving crane 12 which is revolvinglymounted on a circular beam to the top of the reactor building.

FIG. 2 shows in plan view and horizontal cross-section part of theprimary circuit comprising the loop in which a section 10 of primary leg8 has to be replaced, and the concrete bunkers, 13 and 14 respectively,bounded by concrete walls within the reactor building within which steamgenerator 3 and primary pump 4 in the loop of the primary circuit arehoused. Hot leg 6, cross-over leg 7 and cold leg 8 connecting the outletof the primary pump to reactor vessel 5 are shown in plan.

FIG. 2 also shows the pipes of the auxiliary or back-up circuits of thenuclear reactor which are connected to the cold leg at a branchconnection or which follow a route passing above the cold leg.

At least some of these pipes in the nuclear reactor's auxiliary andback-up circuits will have to be cut in order to allow section 10 of thenuclear reactor's cold leg to be replaced.

In the cold leg three branch connections 16 a, 16 b and 16 c which makeconnections between the pipes of the auxiliary and back-up circuits andcold leg 8 are located at the top of the cold leg in the vicinity of thepipe connecting to volute 9 of the primary pump.

Branch connection 16 a provides a connection to a three inch diameterline of the chemical and volume control (RCV) circuit of the nuclearreactor. Branch connection 16 b provides a connection for a pressuriserspray line of the nuclear reactor having a diameter of four inches andbranch connection 16 c provides a connection to a two inch diameter lineproviding a by-pass between cross-over leg 7 and cold leg 8.

Branch connection 16 a connected to the pipe of the RCV circuit is usedto reintroduce water which has been processed in the RCV circuit intothe primary circuit. The injection of a flow of water into the cold legat a temperature which is different from the operating temperature ofthe primary circuit can give rise to some deterioration, such as crazingof the inner surface of the cold leg in the part close to branchconnection 16 a, as a result of which it may be necessary to remove asection 10 from the cold leg extending on either side of branchconnection 16 a for expert examination, the results of which examinationmay result in the systematic replacement of sections of the cold legs ina set of nuclear reactors.

A branch connection 17 of a size substantially larger than branchconnections 16 a, 16 b and 16 c is also attached to the cold leg toprovide a connection for a pipe of the reactor safety injection circuitwhich has a diameter of 12 inches (approximately 300 mm).

Section 10 which is to be replaced in the cold leg generally liesbetween the delivery pipe of volute 9 of the primary pump to which thecold leg is connected and a part of the cold leg located slightlyupstream from branch connection 17 for the safety injection circuit. Thesecond end part of section 10 is selected in such a way that branchconnection 17 for the safety injection circuit lies on a remaining partof the cold leg and cutting and remachining of the connecting end of theremaining part are carried out in a zone in which two parts of the coldleg are connected by welding. In this situation the length of the coldleg which has to be replaced is approximately 3500 mm long, this lengthmaking it possible to replace the entire zone of the cold leg which islikely to have suffered damage through crazing of its inner surface.

The pipes in the auxiliary circuits of the nuclear reactor whichinterfere with the procedure for replacing section 10 of the cold legalso include a pipe 18 of the RCV circuit whose path runs over one endof section 10 which is to be replaced.

The pipes in the primary circuit and the pipes in the auxiliary andback-up circuits are protected and thermally insulated and in particularare surrounded by lagging. Before any work can be done on the primarycircuit and on the pipes of the auxiliary and back-up circuits all thelagging around the cold leg and the auxiliary and back-up pipesmentioned above has to be dismantled in a first stage of the replacementprocedure according to the invention.

It is also necessary to ensure that the lagging surrounding the primarymotor/pump unit comprising the volute and the drive motor of primarypump 4 is dismantled.

These operations for starting the replacement procedure according to theinvention are carried out after cold shutdown of the nuclear reactor,the primary circuit being filled with cooling water at a temperaturewhich is the ambient temperature of the reactor building.

Before carrying out the work on the nuclear reactor according to theinvention, the reactor site is provided with all the components whichhave to be replaced in the auxiliary and back-up circuits, and inparticular the seals. All scaffolding necessary for work in bunkers 13and 14 of the reactor building is also installed.

Various operations are also necessary to ensure that the electricalcables and in particular the measurement cables connected to probes orsensors in the primary circuit in the zone being worked on aredisconnected.

The positions of the various pipes on which work has to be carried outand the volute of the primary pump are surveyed by a topographic survey.

FIGS. 3 and 4 illustrate the environment in which work has to be done oncold leg 8 within bunker 14 for primary pump 4. The primary pump hasbeen illustrated only as the shape of volute 9, the drive motor unit andthe pump impeller having been dismantled so that the top of primary pump9 comprises the plane of the horizontal joint 9 a of volute 9. Forsimplification, the cross-over leg connected to the inlet pipe of volute9 is also not shown. At the top of bunker 14 the reactor building has aconcrete wall 21 which will be used for the attachment of handling meansfor implementing the procedure according to the invention, asillustrated in FIG. 5. A concrete beam 20 of the reactor building whichis in a horizontal position is also located above a part of the coldleg, in the vicinity of branch connections 16 a and 16 b.

The part of the cold leg facing the exit from primary pump bunker 14includes a branch connection 17 providing a connection to injection line17′ and a second branch connection 19 for a pipe of the safety injectioncircuit.

Various floors or floor gratings are located within space 14 and inparticular a platform 22 is provided above the joint plane 9 a of volute9 of the primary pump.

As can be seen in FIG. 5, a monorail 24 is secured in a horizontalposition above the primary pump through a plate 23, and on this monorailis fitted a hoist 24 a which can lift and convey loads of a mass up to10 tonnes within primary pump room 14. Monorail 24, which is parallel tocold leg 8 and which is located vertically above the cold leg, comprisesa cantilevered portion above the exit from primary pump room 14, so thatthe monorail will allow hoist 24 a which is mounted on a carriage tomove along beam 24 to the end of beam 24 constituting the monorailvertically above the end of section 10 of cold leg 8 which has to bereplaced.

Hoist 24 a and monorail 24, having a capacity of 10 tonnes, inparticular make it possible to handle the section of the cold leg whichhas to be replaced. After monorail 24 has been fitted, tests areperformed to check that it is in satisfactory working order and willbear to the loads which will have to be handled.

The auxiliary and back-up lines of the reactor circuit connected to thecold leg or located in the vicinity of the cold leg are then supportedand the positions of the cuts which have to be made on these auxiliaryand back-up lines are then marked before cutting with an automaticcutting machine.

In particular pipe 18 passing over cold leg 8 is cut to permitsubsequent operations for the support of cold leg 8.

After making cuts in the auxiliary and back-up pipes which are necessaryin order to implement the procedure according to the invention, the cutends are then blanked off to prevent any cooling water from exiting viathe cut zones, the primary circuit being still full of cooling water.

After making measurements, the replacement pipe sections for theauxiliary and back-up circuits are prefabricated.

A dimensional survey is then carried out on the part of the primarycircuit on which the work is to be done, and in particular on the coldleg, and the cold leg is supported in the position identified by thetopographic survey.

FIGS. 2 and 6 show the elements supporting the cold leg which inparticular comprise horizontal supporting columns and supporting members25 a, 25 b and 25 c shown in FIG. 2 which support volute 9 of theprimary pump in position.

FIG. 6 shows the supporting components for cold leg 8, at the end ofsection 10 which has to be replaced, comprising a supporting column 26and supporting members 27 a, 27 b, 27 c and 27 d. Supporting members 27a, 27 b, 27 c and 27 d and supporting column 26 are located in a zone ofcold leg 8 which is slightly upstream from branch connection 17 and pipe17′ of the RIS circuit and slightly downstream from the welded zone ofthese two parts of the cold leg in the vicinity of which one of the cutsin the section which has to be replaced will be made.

Supporting members 25 a and 25 c for volute 9 of the primary pumpprovide support in the direction of the cold leg and member 25 bprovides support in a direction at a high inclination in relation to thedirection of the cold leg. The supporting members are supported on theconcrete walls of primary pump room 14 or on beam 20 which passesbeneath the cold leg. Supporting member 25 a which is placed betweenconcrete beam 20 and the connection of cross-over leg 7 of the primarycircuit make it possible to move the pump volute in the direction of thecold leg.

The components wedging the volute of the primary pump are dismantled anda supporting jack is fitted beneath cold leg 8 bearing on beam 20.

A very accurate determination of the cuts which have to be made is thenperformed, for example using a highly accurate metrology tool.

The locations of the cuts which have to be made in order to separate thesection 10 of cold leg 8 which has to be replaced are illustrated inFIG. 3.

A first cut 28 a has to be made in the weld zone between the twosections making up the cold leg and a second cut 28 b has to be made inthe connecting plane between cold leg 8 and the delivery pipe of volute9 of the primary pump.

The cutting planes are marked on the cold leg, in an orientation atright angles to axis 8′ of cold leg 8.

A new replacement section of cold leg 8 of the primary circuitapproximately 350 mm long, fitted with branch connections similar tobranch connections 16 a, 16 b and 16 c in the section of cold branch 8which has to be replaced and a temperature sensor boss 16 d having adiameter of 1 inch located between branch connections 16 b and 16 c, isthen provided.

Branch connection 16 a is constructed by forging the wall of replacementsection 10 for cold leg 8 and branch connections 16 b and 16 c and boss16 d are positioned on and welded to the new replacement section 10 ofcold leg 8.

An orbital cutting machine of the standard type is used to make the cutson the cold leg. This standard cutting machine is normally used toconnect pipes of the primary circuit with narrow bevel welding, thiscutting machine being generally called a mobile narrow bevel machiningunit. All the pipes or ducting which might impede the work of cuttingout and removing the section of the cold leg which has to be replacedare then cut and removed, and then the primary circuit is drained. Thework of cutting the section of the cold leg which has to be replaced iscarried out with the supporting components for the pump volute and thecold leg in place.

The cutting machine of the standard type is placed on the primary leg inthe cutting plane 28 a, on the side of the weld between the two sectionsof cold leg 8.

As illustrated in FIG. 7, various operations are performed on the top ofvolute 9 of the primary pump at the level of joint plane 9 a. First ofall a survey is performed to check that the joint plane of pump volute 9is horizontal, then an interface ring 29 is fitted to protect the planeof the volute joint and to provide further support for the componentsrequired when implementing the procedure according to the invention.

A cover 30 which is of one piece with a water-filled container 30′designed to provide biological protection for the personnel workingabove the top opening of volute 9 of the primary pump is fitted ontointerface ring 29.

As can be seen in FIG. 8, a transfer surface 31 incorporating ahorizontal frame which provides for the movement of loadbearingcarriages is fitted above the pump volute on interface ring 29. Acontainer which is designed to collect radioactive material originatingfrom the cuts made in the various pipes and ducts is also fitted ontransfer surface 31.

A topographic survey of all the pipes in the auxiliary and back-upcircuits which have not yet been cut is then performed and the cutswhich are to be made are accurately marked out. The cuts are made andthe cut sections, which can be placed in the container, are removed. Thecutting lines on the pipes in the auxiliary and back-up circuits areestablished on the basis of the parts of these pipes which will berecovered and the parts which will actually be replaced.

After the cuts have been made in the auxiliary and stand-by circuitpipes they are blanked off and then the pipe ends to which thereplacement sections will be connected by welding are bevelled.

A platform 22 is fitted above the volute of the primary pump and section10 of the cold leg which has to be replaced is then cut along cuttingplane 28 a on the side of the weld of the cold leg sections.

Containment is provided for the cut zone of the cold leg and supportingmembers are welded to the remaining part of the cold leg on the side ofreactor vessel 5.

The cutting machine is mounted on cutting plane 28 b on the side ofvolute 9 of the primary pump and the second cut is made in section 10which has to be replaced. Containment is also provided for the secondcutting zone.

Hoist 24 a of monorail 24 is located above section 10, which is slungonto the lifting cable of the hoist.

A storage container for section 10 of the primary leg which has to bereplaced is then brought into the reactor building and the container isset down on transfer surface 31 resting on the volute of the primarypump. The storage container is moved laterally to bring it into linewith the axis 8′ of cold leg 8, vertically above section 10 which has tobe replaced.

Section 10 which has been cut out is lifted using hoist 24 a of monorail24 and cut section 10 is moved laterally above transfer surface 31.Section 10 of the cold leg is placed in the storage container resting ontransfer surface 31. The ends of section 10 cut from the cold leg can beblanked off to provide biological protection and temporary containmentand lead sheeting providing biological protection can be placed on thesection to confine the section within the storage container. Thecontainer is moved laterally on the transfer surface by a distance ofapproximately 400 mm and the lid of the container is fitted, closed andlocked. The section confined in the container is removed from thenuclear reactor using polar crane 12. The supporting jack for thesection located on concrete beam 20 is removed. The worn-out section isremoved from the reactor building and the cutting machines are alsoremoved from the spaces in the reactor building.

The remaining parts of the cold leg on the vessel side and on theprimary pump piping side can be temporarily blanked off.

The ends of the remaining part of the cold leg on the vessel side andthe primary pump delivery pipe side are then decontaminated, togetherwith the inner surface of the volute. For this purpose temporaryblanking off means are fitted to the remaining part of the cold leg onthe reactor vessel side and the pipes of the volute. Decontaminationcontainment is then placed around the components which have to bedecontaminated and a chemical etching solution is caused to circulate incontact with the surfaces requiring decontamination.

After decontamination the decontamination containment is dismantledtogether with the temporary blanking off means for the cold leg and thevolute and, as shown in FIG. 9, a protective basket 32 is fitted withinthe volute in the suction pipe of the primary pump.

A final operation to decontaminate the inner surface of the volute isthen performed by hand.

After all the equipment required for decontamination has been dismantledand removed a pipe 33 providing biological protection and mechanicalprotection for the surfaces of the volute is fitted into the inner partof diffuser 34 of the primary pump to form an access opening through thetop of the volute of the vertical axis pump.

Vinyl containment 35 is also placed around diffuser 34 to ensure itscontainment.

Dose monitoring is performed to determine whether it is possible to gainaccess to the site for further operations.

The ends of the remaining parts of the cold leg are inspected byradiography. Any repairs are made by filling if there are any defects orlack of thickness in the parts.

A machine for bevelling pipe ends is then located on the end of theremaining part of the cold leg on the vessel side and a bevel is made onthis end, which will form one of the two narrow bevel surfaces forwelding the end of the replacement section. A check is made to ensurethat the original weld between the two sections of the cold leg wherethe cut was made along cutting plane 28 a has been completely removed.

A bevel is then made on the delivery pipe of the primary pump volute anda dimensional check is then made on the two bevels using penetratingdye.

After the bevelling machines (BM) have been removed, means to isolatethe connecting ends of the remaining parts of the cold leg are fitted onthe vessel side and the primary pump volute side.

It is then a question of fitting and welding a new section of theprimary leg, similar to section 10 which has been cut out and removed,into position and welding it to the ends of the remaining parts of theprimary leg. As indicated above, the new section incorporates branchconnections for the auxiliary and back-up circuit pipes connected to thesection of the cold leg and is of excess length in comparison with thesection which has to be replaced.

Reference and measurement operations are first of all performed.

A target-holding jig is located on each of the machined bevels of theremaining parts of the cold leg, on the vessel side and the volute side.A topographical survey of the relative initial positions of the twobevels is performed. The volute of the primary pump is moved to atheoretical abutting position, taking into account the predeterminedwelding shrinkage for each of the welds.

A second topographical survey of the relative positions of the bevels isperformed.

Two supporting and guide rings are then fitted onto the ends of theremaining parts of the cold leg and a topographical survey is made ofthe new replacement section.

To begin with the new replacement section is adjusted for length on thebasis of the topographical survey of the relative positions of thebevels on the remaining parts of the cold leg. Bevels are machined atthe ends of the new replacement section so that the bevelled surfacesmade form two narrow connecting bevels for replacement section 10 withthe bevelled surfaces of the ends of the remaining parts of the cold legwhen the replacement section is fitted into place.

After the end bevels of the replacement section have been machined, thenew replacement section which is equipped with a supporting and guidering at each end is placed in position. The volute of the pump is placedin the abutting position using the supporting device described above.Before being fitted into place the new replacement section is equippedwith internal means to provide an argon chamber for welding.

As can be seen in FIGS. 10A and 10B, two supporting struts 36 which areheld in place by a plate 36′ fixed to beam 20 (see in particular FIG.11) are positioned beneath the zone where the new replacement section ofthe cold leg will be received close to concrete beam 20.

The rest of the primary leg is supported by supporting strut 26 whichwas first placed in position together with supporting means 27.

As can be seen in FIG. 10A, the new replacement section 10 is loweredinto the reactor building from an entry airlock into the reactorbuilding by the rotating crane as shown by arrow 39 a, until it rests ona docking surface 38 set down on transfer surface 31.

The docking surface is then moved laterally (arrow 39 b) to place newreplacement section 10 in axial alignment with the remaining parts ofprimary leg 8.

The new replacement section is of one piece with a cradle of dockingsurface 38.

The unit comprising the new replacement length, the cradle and dockingsurface is picked up using hoist 24 a to set it down on struts 36 andbeam 20 as shown in FIGS. 10B and 11. The corresponding movements areshown by arrows 39 c and 39 d in FIG. 10A. Volute 9 of the primary pumpis moved by a maximum amount established by calculation to ensure thatthe new replacement section can be inserted. The connecting ends of thenew replacement section and the ends of the remaining parts of the coldleg are accurately offered up to each other. The new replacement sectionof the cold leg which, as shown in FIG. 11, includes supporting andguide rings 37 a and 37 b respectively at each end is adjusted andsecured in position.

The means supporting pump volute 9 are released for adjustment and finalpositioning.

Replacement section 10 is placed and secured in position as shown inFIG. 11.

The ends of replacement section 10 are then welded to the ends of thecold leg which have remained in situ using a narrow bevel orbital TIG(NBOT) welding procedure.

As shown in FIG. 11, the NBOT welding machine is positioned and adjustedon each of supporting and guide rings 37 a, 37 b at the ends ofreplacement section 10.

The two ends of the replacement section are then welded to a thicknesscorresponding to a fraction of the total thickness of the primary pipeforming the cold leg, by partial filling of the narrow bevels with weldmetal, the welded thickness being for example from 15 mm to 25 mm.Shrinkage at the joints is monitored by moving volute 9 with the help ofthe supporting means throughout the welding operation.

After the new replacement section has been partly welded at its ends,topographic surveys of the positions of the bevels, the branch pipes andunconnected pipes of the auxiliary and back-up circuits of the nuclearreactor are performed so that the replacement pipes can be adjusted forlength.

Any means which may be within the cold leg on the primary pump side aredismantled to leave space available for inserting a machine for carryingout work within the cold leg.

In fact, as indicated above, in order to obtain a perfect condition ofthe internal surface of the primary leg at the welds connecting thereplacement section it is necessary to perform a grinding machiningoperation on the inner part of the joint welds, within the primary leg,using means whose movements and positioning are remote controlled andwhich are preprogrammed to carry out a grinding operation on the innerpart of the joining welds.

FIGS. 12 and 13 show the components located above or within the volutewhich make it possible to insert and move means for working within thecold leg of the primary circuit in which the new replacement section hasbeen partly welded.

FIGS. 12 and 13 show volute 9 the primary pump into which means 40 forcarrying out work are inserted into the delivery pipe 9 b of volute 9 towhich the replacement section (not shown) is connected by a partialweld.

As indicated above, a protective pipe 33 which rests on interface ring29 at the top of volute 9 has been fitted within diffuser 34 of thepump. A protective basket 32 has also been fitted in the suction pipe ofthe volute. Transfer surface 31 rests on interface ring 29 and permitsmovement in a horizontal direction by a lift 41 carried by a movingtable 42 moving in a direction in the horizontal plane parallel to thecold leg. A gangway 43 to receive means 40 for carrying out work hasalso been fitted within the volute so as to extend the lower surface ofthe inlet part of pipe 9 b communicating with the cold leg. Means 40 forcarrying out work supported by a supporting plate of lift 41 ispositioned on gangway 43 at the inlet to pipe 9 b by vertical movementsof lift 41 and horizontal movements of table 42, as shown by doublearrows 44 a and 44 b.

FIG. 14A shows means 40 for carrying out work which includes three mainparts, a programmed and remote controlled working robot 45, a crawler 46(shown separately in FIG. 14B) and a support 47.

As can be seen in FIG. 14B, crawler 46 is constructed in such a way thatthe means for carrying out work can be moved within a pipe.

Means 46 incorporates two sets of wheels 46 a and 46B whose spacing andinclination with respect to a median plane of crawler 46 can be adjustedso as to adjust the crawler to pipes of different inside diameter.

The crawler has a platform 48 which is designed to receive support 47onto which robot 45 is secured.

Each of the sets of wheels 46 a and 46 b of crawler 46 include anindependent drive motor 49 mounted on the axis of one of the wheels inthe sets of wheels. Motor 49 is remote controlled to move the crawlerand the means for carrying out work within the pipe in which the work iscarried out.

Each of the sets of wheels may comprise two pulleys rotatably mounted onthe mechanical structure of the set of wheels and a belt of toroidalshape passing over the two pulleys. Each of the wheels in the sets ofwheels may also constitute an independent wheel incorporating a toroidaltire.

Support 47 comprises a structure 47 a in the form of a plate which canbe placed and secured on plate 48 of crawler 46. Two shoes 47 bassociated with jacks acting in a direction to extract or retract theshoes and a locking shoe 47 c associated with a jack which can beactivated in a direction parallel to and in a direction opposite to thedirection of action of shoes 47 b are mounted on the structure 47 a ofsupport 47.

When crawler 46 reaches the area where work has to be carried out,movement of the crawler being remote controlled, the crawler is stoppedand the jacks of the supporting device are activated so as to placemeans 40 for carrying out work in a fixed position within the pipe,supporting shoes 47 b bearing against part of the pipe, for example alower part, and locking shoe 47 c bearing against an opposite part ofthe pipe, for example an upper part.

Structure 47 a of supporting means 47 comprises rapid connection meansfor robot 45 which may for example comprise dovetailed means ofassembly.

The structure of the supporting means which is of one piece with plate48 of the crawler also supports a tool magazine from which robot 45 cansuccessively choose the working tools necessary, for example in the caseof an operation which requires several successive stages using differenttools.

Robot 45 is an arm of the anthropomorphic type having six axes ofmotor-driven rotational movement, the arm incorporating an end part 45 abearing a rapid attachment device for tools of the automatic type whichcan be operated remotely to ensure that a tool is picked up or replacedin the course of a complex operation within the pipe.

Such a robot arm of a standard type has for example been described inFrench patent 2,780,907 filed by the FRAMATOME company.

As indicated above, before carrying out work within the pipe, forexample an operation of machining the inner part of the welds joiningthe replacement section of the cold leg, it is necessary to insert themeans for carrying out work into the entrance to the pipe and then tocontrol its movement within the pipe to the area where the work has tobe done and finally to secure it in its working position through theshoes of the supporting device.

When work is carried out within the cold leg of the primary circuit itis possible, as indicated above, to insert means 40 through the volute 9of the primary pump. However, in the case of nuclear reactors having apower of 900 MWe, because the pump diffuser is kept in place, the meansfor carrying out work cannot be lowered and located at the entry to thepipe connecting the volute to the cold leg in a single piece.

In this case, initially robot 45 is located on support or gangway 43 atthe entry to the pipe and then the carriage and the support are loweredinto the volute. An operator then descends within the volute and ensuresthat robot 45 and support 47 are coupled and that the assembly islocated at the entrance to pipe 9 b of the volute. Robot 45 is loweredon the plate of lift 41 borne by a carriage which permits it to move asfar as gangway 43. Coupling of robot 45 to support 47 is very quick, sothat the work by the operator within the volute only requires a veryshort time of less than one minute. The assembled means 40 for carryingout work in position at the entrance to the delivery pipe of the primarypump is remote controlled to move it within the cold leg. In order to dothis means 40 is connected to a set of cables and conduits which providea power supply to independent drive motors 49, the jacks of the support,the rotational movement motors of the components making up the robot armand the tools fixed to the end 45 a of robot arm 45. The fact that drivemotors 49 for wheel sets 46 a and 46 b of crawler 46 are independentmakes it possible to move the crawler along a route which is notnecessarily straight.

When means 40 for carrying out work moved within the pipe by crawler 46reaches the area where work has to be done, crawler 46 is caused to stopby remote control and shoes 47 b and 47 c of supporting device 47 areplaced in a supporting position. Means 40 for carrying out work is thuspositioned within the pipe in an area where work is required.

It would be possible to position means 40 within the cold leg in asingle piece, by introducing the means comprising the robot arm, thesupport and the crawler assembled together in an open end of the coldleg within the nuclear reactor vessel. Means 40 could be lowered intothe vessel by a lift similar to lift 41 and placed on an access gangwayat the entrance to the pipe in the vessel which connects to the coldleg.

In any event means 40 for carrying out work is positioned in such a waythat an operation to machine the inside part of the junction welds forthe replacement section of the cold leg can be carried out. The junctionwelds are machined and inspected on the pump volute side and the vesselside one after the other.

FIG. 15 shows part of the joint in the primary pipe in which means 40for carrying out work has been positioned and secured in place asdescribed previously. So that means 40 for carrying out work can be seenwithin primary leg 8 only a very short section of thee remaining part ofthe cold leg to which replacement section 10 has been fixed by weldingas described previously is shown.

Supporting shoes 47 b are in the low position and bear against the lowerpart of the inner surface of the primary leg, while a locking shoe 47 cis extended to bear against the upper part of the inner surface of thecold leg. In this way means 40 for carrying out work is perfectlysupported in a working position within the cold leg.

A tool 50 comprising a grinding milling cutter and motor drive issecured to the end 45 a of the robot arm which makes it possible toorient the milling cutter of tool 50 and place it in a position fromwhich the inner surface of junction weld 51 between the replacementsection on one of the remaining parts of the cold leg can be ground. Inorder to carry out grinding the tool is located and at all times held ina machining position by the robot arm which is caused to rotate by ahalf-turn about an axis in line with axis 8′ of cold leg 8 to grind ahalf-circumferential part of weld 51.

Grinding is carried out in successive passes by causing the tool torotate about axis 8′ of cold leg 8 in a single direction, the tool beingreturned to its initial position by the robot arm through high speedrotation at the end of each grinding pass.

The operations of positioning the means for carrying out work andmachining by grinding are continuously monitored on a screen locatedoutside the working area on which images of the working area provided bya video camera associated with tool 50 carried by the robot arm aredisplayed.

Initially the inner part of the partial welds on the replacement lengthof the primary pipe is therefore ground, these welds having beenpreviously made by filling an inner part of the bevel made between thereplacement section and the end of a remaining part of the primary pipe.

Grinding of the inside part of the weld-connecting the replacementsection of the primary pipe is carried out in a programmed way, thevarious successive stages in grinding being performed automatically oneafter the other.

After the operation of grinding the internal surface of a weld, theshape of the ground surface is inspected using a measuring tool which istaken up by the robot arm on the support after the grinding operationhas been completed. This operation can also be performed in a programmedand automatic way.

The weld area of the inner surface of the cold leg is then cleaned aftergrinding followed by inspection of the ground and cleaned inner surfaceof the weld using penetrating dye. In order to do this robot arm 45 iscontrolled so that its end part 45 a is equipped with the tools used insuccession to carry out the successive operations necessary to performthe inspection using penetrating dye. These successive operationscomprise applying a penetrating dye to the area under inspection,removing the surplus dye by wiping, drying the area inspected, remotevisual inspection of the inspected area to check that any surplus dyehas been removed, applying a developer to the inspected area and remotevisual inspection of the inspected area to determine whether any defectsare present, the remote visual inspections being carried out by camerasassociated with the tools used for the penetrating dye check and pickedup in succession by end 45 a of robot arm 45.

The images displayed by the camera are displayed on a television screenin an inspection area at a distance from the area where the work isperformed.

Radiographic inspection of the partial welds of the replacement sectionin the cold leg is also performed before completing filling of the weldbevels of the two welded joints for the replacement section.

Internal cleaning of the welds is then performed using theremote-controlled and preprogrammed means 40 for carrying out workwithin the primary pipe. The whole of the inside of the cold leg is alsocleaned. Then the interior of the weld zones is inspected using theremote controlled and preprogrammed means for working within the primarypipe in the same way as when inspecting these weld zones after partialwelding.

After the welding means and their supports on the outside of the primarypipe have been dismantled, external grinding of the welds and theninspection of the welded zones using penetrating dye is performed on theoutside of the primary pipe, it being possible for this inspection to beperformed manually. Finally a radiographic inspection of the completedwelds is performed.

The operations carried out within the primary pipe for correcting theinner parts of the welds by grinding and the inspections and finishingoperations on the inner part of the partial welds make is possible toensure that the inner parts of these welds are of perfect quality andthat there is a complete absence of defects on the surface which comesinto contact with the primary water in the course of the operation ofthe nuclear reactor.

Furthermore, inspection of the inner parts of the welds carried out bythe tool makes it possible to check that no defect has been introducedas a result of the final welding operation.

After the welds of the replacement section have been made and inspected,the tools used, such as the tools to support the cold leg and thepositioning cradle and the struts supporting the replacement section,are removed.

The lengths of the nuclear reactor auxiliary and back-up lines which hadto be cut in order to fit and fix the replacement section of the coldleg are then replaced or repositioned.

After all the auxiliary lines have been restored, various operations todismantle and remove the components required for the work which haveremained in position, such as the biological shield placed in theprimary pipe on the vessel side and the transfer frame mounted on top ofthe pump volute, are carried out. The components inserted into the pumpvolute, such as the protective basket and the vinyl film protecting thediffuser, are also dismantled and removed. A remote visual examinationof the interior of the primary pump volute is performed to check thatthe system is clean and then the pipe protecting the diffuser of theprimary pump and the interface ring are dismantled before refitting thewater guide within the volute. The joint plane of the volute is checkedto ensure it is horizontal and the joint plane is cleaned beforerefitting the pump impeller and the pump drive motor.

The final reassembly operations on the auxiliary and back-up circuitlines are performed before ensuring that the primary pump isreassembled. The primary circuit can then be placed back in service.

The procedure according to the invention therefore makes it possible toreplace a section of a cold leg in a nuclear reactor ensuring that theconnecting welds for the replacement section are perfectly made.

These results are achieved in particular using means for carrying outwork which is inserted into the primary pipe to carry out machining andinspection operations. This means which can be inserted into the primarypipe via a component such as the primary pump or the reactor vessel canbe controlled wholly automatically by remote control, in particular forpositioning the means in the working position within the primary pipe.The operations performed in the working area are generally carried outin a programmed and automatic way following a predetermined or remotelyoperated sequence. In the case of remote operation using a robot such asthe robot arm described above, the latter accurately locates itsconnecting support to the structure of the supporting means in space inan initial stage using a position sensor fixed to the end part 45 a ofthe arm.

The invention is not restricted to the embodiment which has beendescribed.

Thus the means for carrying out work can be used to carry out operationsother than grinding and inspection of the inner part of the welds of thereplacement section for the primary pipe.

The means for carrying out work may be constructed in a manner otherthan that described and may incorporate any means for carrying out work,remote control or programming to carry out any machining or inspectionwork on the inner parts of the welds of the replacement section.

The means for carrying out work may also perform other operations suchas the filling of defective zones within the primary pipe aftermachining.

In this case, instead of replacing a defective section of the primarypipe, a defective section of the primary pipe which incorporatesdefective areas on its internal surface can be repaired. After thedefective areas have been identified through an inspection operation,the defective areas are machined and filled by welding, followed byfinal inspection. In order to perform these operations within theprimary pipe the means for carrying out work described above is used,and this is used in the same way as in the case of machining, inspectingand finishing the welds for a replacement section.

In general, the procedure and the means according to the invention maybe used not only to effect the replacement of a section of a cold legbut may also be used to effect the replacement of a section of any legin the primary circuit of the nuclear reactor.

In the case of a leg which incorporates curved parts, like thecross-over leg, it is possible to use the means for carrying out workdescribed, inasmuch as the crawler which incorporates two sets ofindependent motor-driven wheels can be moved within the curved parts ofthe pipe.

The invention applies to any nuclear reactor incorporating pipes oflarge dimensions used for the circulation of a liquid cooling thereactor core.

1. In a nuclear reactor, cooled by pressurized water, an apparatus forreplacing a section of a primary circuit primary pipe that interconnectsfirst and second components of a primary circuit, the apparatuscomprising: means for cutting out a section of the primary pipe; meansfor removing the cut primary pipe; means for supporting the end parts ofa new replacement section in a position held by the removed pipe; meansfor bevel welding the end parts of the new replacement section of theprimary pipe to confronting corresponding ends of remaining primarypipe; means for working within the pipe along the entire length of theinterior surface of the primary pipe; and means for introducing theworking means through one of first and second components of the primarycircuit to a location within the welded replacement pipe section.
 2. Anapparatus according to claim 1, wherein the working means comprises: ananthropomorphic robot arm, a support, means for securing the robot armand a carriage to the support for moving the support and the robot armwithin the primary pipe and two sets of wheels and drive motorsproviding a rotational drive to at least one wheel in each set of wheelsof the carriage for moving the carriage within the primary pipe.
 3. Anapparatus according to claim 2, wherein the support comprises astructure for supporting the robot arm, two supporting shoes controlledby jacks and one locking shoe controlled by a further jack which bearsagainst opposite parts of the inner surface of the pipe.
 4. An apparatusaccording to claim 1, wherein the means for introducing the workingmeans comprise a transfer surface for lateral movement in a horizontalplane on which there is movably mounted, in a direction in thehorizontal plane, a supporting table and a lift for moving a supportingplate for the working means borne on the supporting table in a verticaldirection, the transfer surface being secured above a horizontal surfaceof the first or second components of the primary circuit through whichthe working means is introduced into the primary pipe through a verticalaxis opening providing access to an internal part of a component of theprimary circuit communicating with the interior surface of the primarypipe.
 5. An apparatus according to claim 1, wherein an access gangwaycommunicates with the interior surface of the primary pipe.
 6. Anapparatus according to claim 1, wherein the first or second componentthrough which the working means is introduced is chosen between either areactor vessel or a primary pump of the nuclear reactor.
 7. An apparatusaccording to claim 1, wherein the working means comprise means to carryout at least one operation of machining, inspecting or welding an innersurface of the bevel welded end parts of the new replacement section andthe ends of the remaining parts of the primary pipe.
 8. An apparatusaccording to claim 1, wherein the means for bevel welding weld the endparts of the new replacement section to the ends of the remaining partsof the primary pipe while the supporting means support said end parts inposition.
 9. An apparatus according to claim 2, wherein the armincorporates an end part bearing an attachment device for automatictools.
 10. An apparatus according to claim 2, wherein the arm has sixaxes of motor-driven rotational movement.